The invention relates to a circuit arrangement for regulating currents flowing through windings of stepping motors, the latter having access only to a common winding neutral point or to partial neutral points.
As is known, stepping motors are used as axle drives for machine tools, peripheral equipment for computers, and the like. Such stepping motors require a circuit which on the one hand permits the current in the individual motor windings to rapidly rise to the required value in the prescribed sequence, and on the other permits the current to drop to zero again after a given specified time.
A known circuit for fulfilling these requirements is an R-L circuit, in which an ohmic resistor is connected in series with the motor winding and a high voltage is applied to this combination.
The resistor has two actions. It limits the current to the necessary value and ensures a small motor time constant in accordance with the law .tau.=L/R, leading to a rapid rise in current. In order to obtain a rapid breaking of the current, a resistor or a Zener diode is connected in series with a normal diode in the free running circuit. This circuit is described in the book entitled "Das Schrittmotoren-Handbuch" ("Stepping Motor Handbook") by the firm Sigma Instruments, European Office, vol. 1973, Publishers G. Schubert and C. Munich 5, *266223 on pages 46 ff. Circuits b, c and d described on page 47 of this book will not be considered here because they require the use of motors which permit separate access to all the ends of the windings.
Other circuits for motors with a neutral point use the chopper principle (described on page 58 of the above-cited handbook), but still use series resistors or Zener diodes in the free running circuit. The efficiency of such circuits is naturally low, because in the series resistors of the closed free running circuit the motor current produces dissipated heat.
It would be advantageous for stepping motors of the type which only permit access to the winding neutral point to have a circuit which permits a rapid switching ON of the current to the desired values, ensures small losses during the desired current flow time, and permits a rapid switching OFF of the current at a selected time with a similar high efficiency to that of the chopper circuits referred to above. However, in the latter circuit, free access to all the ends of the motor winding is assumed.